Direct measurement of local instantaneous laminar burning velocity by a new PIV algorithm

Abstract

Balusamy, Saravanan Cessou, Armelle Lecordier, Bertrand 8th International Symposium on Particle Image Velocimetry (PIV 09) Aug 25-28, 2009 Melbourne, AUSTRALIA SiThis paper presents a new experimental approach using PIV technique to measure the local instantaneous laminar burning velocity of a stretched premixed flame. Up to now, from experimental techniques, this physical property was only accessible in average and the instantaneous interactions of flame with flow structures, mixture variations and walls could not be considered. In the present work, the local burning velocity is measured as the difference between the local flame speed and the local fresh gas velocity at the entrance of the flame zone. Two original methods are proposed to deduce these quantities from pair of particle images. The local flame speed is measured from the distance between two successive flame positions. For the flame localization, a new extraction tool combined with a filtering technique is proposed to access to the flame front coordinates with sub-pixel accuracy. The local fresh gas velocity near the flame front is extracted from the maximum of the normal velocity profile, located within 1 mm ahead of the flame front. To achieve the required spatial resolution, a new algorithm based on adaptive interrogation window scheme has been developed by taking into account the flow and flame front topologies. The accuracy and reliability of our developments have been evaluated from two complementary approaches based, respectively, on synthetic images of particle and on the well-established configuration of outwardly propagating spherical flames. In the last part of the paper, an illustration of the potentials of our new approach is shown in the case of a laminar flame propagating through a stratified mixture

Laminar propagation of lean premixed flames ignited in stratified mixture

“…Since the experiment is conducted of constant volume, the pressure increases after ignition, but this pressure increase is very small, limited to 40 mbars during the flame investigation. Additionally, in this work, the flame burning velocity being calculated directly from the local flame speed and fresh gas velocity, this measurement is not affected by the flame speed decrease due to the limited volume of the chamber in the time range of investigation [25]. Previous experiments in homogeneous mixtures in our combustion chamber have shown that the flame propagation is affected neither by the spark energy nor by the limited volume of the chamber in the time range investigated [25].…”

“…Additionally, in this work, the flame burning velocity being calculated directly from the local flame speed and fresh gas velocity, this measurement is not affected by the flame speed decrease due to the limited volume of the chamber in the time range of investigation [25]. Previous experiments in homogeneous mixtures in our combustion chamber have shown that the flame propagation is affected neither by the spark energy nor by the limited volume of the chamber in the time range investigated [25]. Finally, the combustion images of flame propagation through a stratified mixture field are acquired using the combined PIV-PLIF techniques; as shown in Fig.…”

“…The flame position is localized by the discontinuity of seeding due to the particle evaporation through the sharp temperature gradient of the flame front. Due to the irregularities in the PIV images introduced by the use of discrete particles to seed the gas, an extraction tool of the flame outline has been proposed [25]. This extraction tool, which localizes the flame front with subpixel accuracy and eliminates noises by an adaptive filtering technique, has demonstrated its ability to measure the local flame speed accurately by the determination of the local shortest distance between the flame contours of a couple of PIV images.…”

“…The local fresh gas velocity is measured using a new PIV technique [25], which is based on the adaptive interrogation window scheme. The new algorithm combines a new window interrogation arrangement taking into account the flame front shape, the flame front displacement, and the gas expansion with an original particle-matching algorithm extracting the velocity ahead of the preheat zone along the normal to the flame front [25]. This algorithm provides a velocity profile with a high spatial resolution while keeping a large field of view.…”

“…Then simultaneous PIV-PLIF images of laminar flame propagation are acquired for three different stratified mixture configurations. From the PIV images, the local values of flame speed, fresh gas velocity, and laminar burning velocity are measured using a new PIV algorithm [25]. The flame properties are analyzed according to the local stretch rates once the flame propagates in the homogeneous lean mixture.…”